This invention was born of the need for a robust and compact three dimensional mass spectrometer having a low weight and low power requirement for use in space. These characteristics of the invention also make it quite useful in certain earth based applications. It can identify atoms and molecules and distinguish between them.
The function of this mass spectrometer in space is to analyze the types of ionized particles in the region of the spacecraft on which it is mounted. A great deal can be learned about the interactions of planetary magnetospheres with a planet's atmosphere and the solar wind by analyzing the types of particles in the different regions of space around and between the planets. Different ion species come from the sun than from the upper atmosphere of a planet or off the surface of a moon and composition characterizes the source of the local plasma. These interactions and sources are very important to understand because they contributed to the radiation environment as well as telling us about the composition of local bodies.
This mass spectrometer is suitable for any space mission in which measurements of the local plasma composition are needed. It can be used in many different space plasma regimes by tailoring its field, size, and voltages to the expected plasma energies and densities. In addition, the LEF module of this spectrometer is compatible with many different types of energy analyzers. An energy analyzer is used to feed particles to the LEF module for mass analysis. Because the LEF can be used with many different analyzers, instruments in which it is used can be designed to have widely varying sensitivities and fields of view. This is very important, for example, in the case of a spinning versus a 3-axis stabilized spacecraft; to see all of space instruments must have different fields of view.
Most plasmas observed in space contain a variety of particles of different masses and ionization states. A determination of the distribution of mass and charge states often allows one to distinguish between different possible sources and sinks for the plasma and can provide information on the sources which is otherwise not obtainable. Mass spectrometers for measuring space plasma composition have been developed, but to date no instrument has provided the important combination of (1) nearly complete viewing coverage, (2) high temporal resolution (a few seconds) for a mass resolved set of distribution functions, and (3) ultra-high mass/charge resolution over a large energy range.
Space plasma instruments for mass resolved plasma measurements have utilized mainly two techniques: magnetic mass analysis and field-free time-of-flight (TOF) analysis. Magnetic mass spectrometers have certain inherent drawbacks which limit their use for the measurement of hot magnetospheric plasmas. These instruments are expected to measure ions with energies as high as about 50 keV/q. Achieving high mass resolution of particles at this energy level with an instrument that has the necessary very wide acceptance geometry requires a large amount of heavy magnetic material. Also the requirement for high sensitivity, which is needed to make fast measurements of hot diffuse magnetospheric plasmas, competes with the requirement for high mass resolution, since the aperture size needs to be large for the former and small for the latter.
TOF mass spectrometers with essentially field-free flight paths have the advantage that the entrance aperture to the mass resolving region can be much larger than in a comparable resolution magnetic mass spectrometer, thus providing higher sensitivity and a broader energy range for an instrument of a particular size. A main limiting factor for mass resolution in this type of TOF mass spectrometer is the energy spread of the ions entering the timing section of the device. Also, resolution is degraded by path length variations for the timed portion of flight of the ion. Both the magnetic and field-free TOF mass analysis techniques suffer from limitations which reduce the utility for making fast highly mass resolved measurements of the three-dimensional distribution of hot plasmas.
On earth, the inventive mass spectrometer may be used in a laboratory or as a portable instrument for detecting substances in the atmosphere. Virtually every solid material has a vapor pressure, that is, has atoms or molecules of the material present in the form of a vapor in the atmosphere adjacent to the solid material. These atoms or molecules can be captured, ionized, and analyzed to determine what substances were or are present in a room or the immediate atmosphere where a portable instrument is located. Substances such as explosives and narcotics can be detected.